Missing Values: NULL in TypeScript

Sometimes a value is missing. SQL writes a missing value as NULL, like null in TypeScript. In the shop, the Gift card has no category: its category is NULL.

NULL means "unknown", so a comparison with it is never true. category = NULL is unknown for every row, even for the gift card, and WHERE keeps only the rows whose test is true, so it finds nothing. To test for a missing value, SQL has IS NULL, and its opposite, IS NOT NULL:

const query: string = [
  "SELECT name, price",
  "FROM products",
  "WHERE category IS NOT NULL",
].join(" ");

This query keeps the 7 products that have a category. In this lesson you write two queries, and the check prints both, with show(db, query) and show(db, query2). Your code must print exactly this:

name | category
(0 rows)

name | category
Gift card | NULL
(1 row)

Your task: the connection db to shop.db is already there. In query, look for the products without a category with = NULL and see that it finds nothing. In query2, find them the right way, with IS NULL.

Assignment
Follow the Coding Tutorial to write both queries, one clause per line: SELECT, FROM, then a WHERE.

Hint
Inside the SQL, NULL goes without quotes: 'NULL' in quotes is just a four-letter text. query2 has the same SELECT and FROM lines as query; only the WHERE changes. Each clause is its own string in the array, with a comma after it: .join(" ") puts a space between them, so the clauses don't run together.